The present invention relates to a projection exposure apparatus and method used when transferring a projection master plate (mask, reticle and the like) onto a substrate in photolithographic processes for manufacturing devices like semiconductor devices, image pickup devices, liquid crystal display devices and thin film magnetic heads, and further relates to an optical system having a folding member suited to the projection exposure apparatus, and a method for manufacturing the optical system.
In photolithographic processes for manufacturing semiconductor devices and the like, a projection exposure apparatus is used that exposes the pattern image of a photomask or reticle (hereinafter, collectively referred to as xe2x80x9creticlexe2x80x9d) as the projection master plate onto a substrate (wafer or glass plate and the like) coated with a photosensitive material like photoresist via a projection optical system.
With the increase in the level of integration of semiconductor devices and the like in recent years, the resolving power required by projection optical systems used in projection exposure apparatuses has been rapidly increasing. To meet this requirement, it has become necessary to shorten the wavelength of the exposure light and to increase the numerical aperture (NA) of the projection optical system. However, if the wavelength of the illumination light is shortened, particularly below 300 nm, the number of types of glass materials that can be used for practical purposes is limited to a few due to the absorption of light. Accordingly, the correction of chromatic aberration becomes problematic if the projection optical system is constructed with just dioptric optical elements. In addition, a dioptric optical system requires numerous lenses to correct the Petzval sum.
In contrast, a catoptric system not only has no chromatic aberration, but can also easily correct the Petzval sum by the use of a concave reflecting mirror. Accordingly, the construction of projection optical systems with so-called catadioptric optical systems that combine a catoptric system with a dioptric system has heretofore been proposed. Such catadioptric optical systems have been proposed in, for example, U.S. Pat. No. 5,537,260, U.S. Pat. No. 4,747,678, U.S. Pat. No. 5,052,763 and U.S. Pat. No. 4,779,966.
An increase in the NA and exposure region of projection optical systems has been demanded in recent years, and the aperture diameter of the optical members that constitute catadioptric optical systems has likewise increased. In light of the resolution required by projection exposure apparatuses, the effect of deformation of large optical members due to gravity cannot be ignored. A catadioptric optical system may be constructed with optical members in which the direction of the optical axes is not identical, as is typical of the prior art. One or more such optical members having power tend to be deformed asymmetrically with respect to the optical axis. This gives rise to asymmetric aberrations, which are difficult to correct during manufacturing, making it difficult to obtain sufficient resolution.
When correcting chromatic aberration in a conventional catadioptric optical system, high-order chromatic aberrations like transverse chromatic aberration, cannot be sufficiently corrected with just a concave reflecting mirror and quartz glass, and the image size cannot be increased. Consequently, attempts are being made to realize satisfactory correction of chromatic aberration over the entire exposure region by forming a number of lenses with fluorite. Nevertheless, since the volume and refractive index of lenses made of fluorite change much more than quartz glass and other optical glasses when environmental factors, like temperature, change, the optical performance of conventional optical systems deteriorates greatly when the environmental conditions fluctuate.
Catadioptric optical systems and catoptric optical systems typically require the use of a folding member to separate the optical path of the going path toward the concave mirror from the optical path of the returning path from the concave mirror. As a result, a plurality of partial optical systems having mutually different optical axes becomes necessary, and it follows that a plurality of lens barrels having different axes becomes necessary. Consequently, there is the problem that, compared with dioptric optical systems, errors are easily generated in the adjustment between the plurality of optical axes when assembling catadioptric optical systems and catoptric optical systems. In addition, even after assembly, the stability is poor due to the complex construction, and the positional relationships between optical axes gradually deviate, creating a tendency for the image to deteriorate. In addition, the folding member has an incident optical axis and an exit optical axis, which are not formed symmetrically. For this reason, rotating the folding member about the incident optical axis or about the exit optical axis due to, for example, factors like vibration, causes rotation of the image. In addition, rotating the folding member about the axis orthogonal to both the incident optical axis and the exit optical axis causes distortion of the image, making it difficult to stably obtain an image of high resolution.
Furthermore, optical adjustment of a dioptric optical system is disclosed in U.S. Pat. No. 4,711,567 and Japanese Patent Application Kokai No. Hei 10-54932, and optical adjustment of a catadioptric optical system is disclosed in U.S. Pat. No. 5,638,223.
The present invention relates to a projection exposure apparatus and method used when transferring a projection master plate (mask, reticle and the like) onto a substrate in photolithographic processes for manufacturing devices like semiconductor devices, image pickup. devices, liquid crystal display devices and thin film magnetic heads, and further relates to an optical system having a folding member suited to the projection exposure apparatus, and a method for manufacturing the optical system.
Accordingly, the first goal of the present invention is to provide a large numerical aperture in the ultraviolet wavelength region, and to achieve high resolution without any substantial impact of gravity and the like.
The second goal of the present invention is to achieve a large numerical aperture in the ultraviolet wavelength region and a large exposure region, and to achieve an optical system of a practical size, satisfactorily corrected for chromatic aberration over the entire exposure region, having stable optical performance even during environmental fluctuations, and having a high resolution.
The third goal of the present invention is to make the optical adjustment of an optical system having a plurality of optical axes easy.
The fourth goal of the present invention is to reduce deterioration in imaging performance even after an optical system having a plurality of optical axes is assembled.
The fifth goal of the present invention is to perform with high precision optical adjustment of an optical system having a folding member.
Accordingly, a first aspect of the invention is a projection exposure apparatus for exposing a mask having a patterned surface onto a substrate having a photosensitive surface. The apparatus comprises an illumination optical system, and a reticle stage capable of holding the reticle so that the normal line of the patterned surface is substantially in the direction of gravity. The apparatus further includes a substrate stage capable of holding the substrate so that the normal line of the photosensitive surface of the substrate is substantially in the direction of gravity. The apparatus further includes, between the reticle and substrate stages, a projection optical system comprising first and second imaging optical systems. The first imaging optical system comprises a concave reflecting mirror and a dioptric optical member arranged along a first optical axis, and is designed to form an intermediate image of the patterned surface. The second imaging optical system has a second optical axis and forms a reduced image of the intermediate image onto the photosensitive surface. A first folding member is arranged in the optical path from the first imaging optical system to the second imaging optical system, and is provided with a reflecting surface having a reflective region that is substantially planar. Also, a second folding member is arranged between the first folding member and the second imaging optical system, and is provided with a reflecting surface having a reflecting region that is substantially planar. The first and second imaging optical systems and the first and second folding members are positioned so that a reduced image of the pattered surface is formed parallel to the pattern surface of the reticle, and the first and second optical axes are positioned so that they are substantially parallel to the direction of gravity.
A second aspect of the invention is a method for exposing a pattern on a reticle onto a substrate. The method comprises the steps of first illuminating the reticle, then projecting an image of the reticle with the projection exposure apparatus as described immediately above, and then exposing the pattern over an exposure region having either a slit-shape and arcuate shape, wherein the exposure region does not include the optical axis of the second imaging optical system in the image plane. In the exposure process, it is preferable to simultaneously scan the reticle stage and the substrate stage.
A third aspect of the invention is a projection exposure apparatus for forming an image of a first surface onto a second surface. The apparatus comprises a projection optical system having a lens, a concave mirror, a folding member and two or more optical axes. An optical member is arranged along each of the two or more optical axes, each optical member being held by a barrel provided along each of the two or more optical axes. Each of the barrels includes one or more lens barrel units each having one or more lens assemblies (or alternatively, lens elements) designed so as to be inclinable and translatable with respect to the optical axis. Also, at least one of the barrels is provided with at least one adjustment apparatus capable of inclining and translating the at least one barrel with respect to the optical axis passing therethrough.